Low-Hysteresis and Lineear Piezoelectric Actuator made from Ultra-fine Particles

当晶体尺寸达到纳米量级时，晶体通常表现出与大块晶体不同的特征。几年来，我们一直在研究铁电微粉中的这种尺寸效应，发现晶体尺寸会影响磁区壁的运动或结晶过程，这就建立了一种合成超细微粉的方法。在本工作中，我们试图改善压电PZT驱动器在位移与外加电压之间的关系中出现的迟滞现象或非线性。铅、钛和锆醇氧化物在有机溶剂中溶解。水解液得到的PZT微粒仍处于无定形状态。在600ﾟC空气中加热5h，可使无定形微粒晶化。晶化温度远低于大块晶体的晶化温度(1280ﾟC)。较低的温度能够获得化学计量组成的陶瓷，因为铅在该温度下不会蒸发。得到的细小颗粒通过热等静压(HIP)被焙烧成陶瓷圆盘。陶瓷型细粉的磁滞非常小，约为1%，远小于传统陶瓷的磁滞(约10%)。扫描电子显微镜观察发现，构成我们陶瓷的小颗粒的典型尺寸为数百纳米。然而，尺寸仍然不够小，不足以抑制磁畴壁的移动。高分辨率的透射电子显微镜观察表明，颗粒中存在着几个纳米的精细结构。因此，细微结构似乎是起始粉末边界的“痕迹”，应该是壁面运动的钉扎点。

Crystals generally show different characteristics from bulk crystals when their sizes become an order of nanometer. We have been studying this 'size effect' in ferroelectric fine particles for several years and found that the crystal size affects the domain wall movements or the crystallizing process,which establishes a method to synthesize ultra-fine particles. In the present work, we have attempted to improve the hysteresis phenomena or the non-linearity appeared in the relation between the displacement and the applied voltage in piezoelectric PZT actuators. Lead, titanium, and zirconium alkoxides are dissolved in an organic solvent. Hydrolyzing the solution gives PZT fine particles which are still in amorphous state. The amorphous fine particles can be crystallized through the heating at 600ﾟC in air for 5h. The crystallizing temperature is much lower than that of bulk crystals(1280 ﾟC). The lowered temperature enables to obtain ceramics of stoichiometric composition because lead does not evaporate at this temperature. Fine particles obtained are calcined through HIP(hot isostatic pressing) to form a ceramic disc. The ceramic form fine-particles shows quite small hysteresis of an order of 1%, much less than that of conventional ceramics(about 10 %). A typical size of the small particles composing our ceramics is found to be several hundreds nanometers by SEM observation. The size is not still enough small, however, to inhibit the domain wall movement. High resolution TEM observations suggest that fine structures of several nanometers exist in the particles. Thus, the fine structure seems to be 'traces' of boundary of starting powders and should act as pinning points of the wall movement.